Electrical network for detecting heat due to various causes



March 18, 1958 c. J. KLEIN 2,827,624

ELECTRICAL NETWORK FOR DETECTING HEAT DUE TO VARIOUS CAUSES Filed 001... 27. r 1955 2 Sheets-Sheet 1 INVENTOR @L/FFORD JOHN'- KLEIN March 18, 1958 c. J. KLEIN 2,827,624

ELECTRICAL NETWORK FOR DETECTING. HEAT DUE TO VARIOUS CAUSES Filed Oct. 27, 1955 I 2 Sheets-Sheet 2 SYSTEM RESISTANCE IN oHMs TIME-DURATION 0F FL ;HT

INVENTOR CLIFFORD JOHN KLEIN United States ELECTRICAL NETWORK FOR DETECTING HEAT DUE TO VARIOUS CAUSES Application October 27, 1955, Serial No. 543,083

12 Claims. (Cl. 340233) The present invention relates to electrical networks which are automatically responsive to temperature conditions, and, more particularly, to such networks which can discriminate between a sudden fire, an overheat condition and a slowly burning fire.

The present invention is primarily concerned with improving heat and flame detecting systems. In such systems, an element is utilized which comprises two conductors spaced apart by a material having an infinitely high resistance at a normal temperature to render it substantially non-conductive to electricity and having the characteristic of being rendered conductive at an abnormal high temperature, and suitable means indicate or operate various devices when the abnormal temperature condition has been detected due to a slowly burning or sudden fire.

Accordingly, the primary object of the present invention is to provide an improved network of such type which is also capable of detecting the presence of an abnormal overheat condition existing independently of a fire.

Another object is to provide such a network which discriminates between a fire and an overheat condition Another object is to provide such a network which discriminates between a fixed temperature fire and an overheat condition.

Another object is to provide such a network which is constructed of a minimum number of relatively inexpensive, lightweight components adapted to be arranged in a compact manner.

Another object is to provide such a network which has a long useful life and requires a minimum of maintenance or repair.

A further object is to provide such a network which has utility in a great many fields of application.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

In accordance with the present invention, it has been found that the foregoing objects can be accomplished by providing a voltage dividing bridge type network which essentially comprises a source of unidirectional electrical current, first and second resistance elements connected in series across the source, parallel third and fourth resistance elements and another resistance element connected in series across the source, the resistance elements having resistance values to provide a pair of voltage dividing bridges normally unbalanced in one direction and the first resistance element being constructed and arranged so that the resistance thereof changes in response to a predetermined condition to another value whereby the bridge is unbalanced in the opposite direction, and an electromagnetically operable device, such as a polarity in dicator or polarity sensing device, connected in voltage dividing relationship across the third element and the atent 2,327,62 Patented Mar. 18, 1958 junction of the first and second resistance elements, and a second electromagnetically operable device connected in voltage dividing relationship across the fourth resistance element and the junction of the first and second elements. In order to discriminate between a sudden fire and a slowly burning fire, a time constant network is connected in series with the first mentioned sensing device.

A preferred embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

Figs. 1 to 4 are circuit diagrams illustrating the essential components arranged in a network in accordance with the invention, under normal and detecting conditions.

Fig. 5 is a graph illustrating the ambient temperature conditions which may occur during the various stages of an airplane while in flight and the temperature resulting from fire and overheat conditions.

Referring to Fig. 1 of the drawings, a network is shown which essentially comprises a source of unidirectional electrical current represented by conductors i0 and 1 a condition sensing resistor shown as a variable resistor 12 (first resistor), a fixed resistor 13 (second resistor), a pair of resistors 14 and 15 (third and fourth resistors), a fixed resistor 16 (another or fifth resistor), a pair of polarity indicators or polarity sensing devices 17 and 18 each having a winding 19, upper and lower contacts 24) or 20a and 21 or 21a and a switch element 22. or 22a, respectively, and a pair of relays 23 and 24 each having a winding 25, switch elements and contacts, as described hereinafter.

The source of current may be direct current from a battery or generator, or rectified alternating current. The conductor 10 is illustrated as being connected to the positive side of the source, and the conductor 11 is illustrated as being connected to the negative side of the source.

The condition sensing resistor 12 may be any element subject to changes in its resistance in response to the particular condition to be detected. For example, such an element may be sensitive to heat, light, humidity or mechanical force. In the illustrative embodiment of the invention described herein, such an element is utilized to detect heat or flame on aircraft, or other craft or vehicles, and comprises two conductors of electricity spaced apart by a thermistor-like material having an extremely or infinitely high resistance at a normal temperature to render it substantially non-conductive to electricity and having the characteristic of being rendered conductive at an abnormal temperature caused by the heat of flame or fire. Such elements are well known in the art.

The resistors 13 and 16 are balancing resistors of the type which do not vary apreciably in resistance with ambient temperature changes and consequently remain in fixed ratio when subjected to temperatures ranging from 65 F. to F.

The resistors 14 and 15 are shown herein as voltage dividers and are adapted to provide a wide range in which the network may be accurately adjusted. These resistors also are practically immune to ambient temperature changes.

The successful operation of such a network depends greatly on the use of the ultra-sensitive polarity indicators 17 and 18 which are adapted to detect the change of polarity of the bridge error when the resistance of the sensing resistor 12 reaches a predetermined value. The switch element of each of these indicators is pivotally mounted for free, torqueless movement thereof and has no appreciable mass. Each switch element is under the control of its winding 19, as indicated by the broken lines, whereby when current flows through the winding in one direction, the switch element engages the lower contact, and, when current flows through the winding in the opnearest parallel with the resistor 14 and in series with the resistor 16. Thus, by connecting one end or terminal of the winding of the polarity indicator 18 to the effective junction of the resistors 15 and 16, that is, in voltage dividing relation with the resistor 15, and the other end or terminal of this winding to the junction of the resistors 12 and 13, a double bridge network is provided in a simple and convenient manner.

The contact 20:: or" the indicator 18 is connected to the conductor through a limiting resistor 26a, and the contact 21a is connected to the conductor 11 by a conductor 27a. One end of the winding of the relay 24 is connected to the switch element 22a of the indicator 18, and the other end of this winding is connected to the conductor 11. A diode 23a is connected across this winding for effecting quick return of the relay 24.

The relay 24 includes a switch element 45 connected to the contact 31 of the relay 23 and adapted to engage a contact 46 connected to one terminal of an alarm device, such as a lamp 47, which has its other terminal connected to the conductor 11 and a second switch element 33a connected to the switch element 22a and adapted to engage a contact 3411 connected to the conductor 10 through a limiting resistor 35a to lock in the relay upon operation thereof.

At about 70 F., the resistors 13, 16 and 12 as previously mentioned, have resistances of 8.2 and 5.0 kilo-ohms and more than 200 megohms, respectively, and the resistor has a resistance of 10.0 kilo-ohms, the resistors 15 and 16 being adjusted in voltage dividing relationship to provide for polarity indicator response at the specified temperature as hereinafter described. Since the resistance of the resistor 12 drops sharply above 500 F., the resistance values in this network enable the indicator 18 to detect a change in polarity in its network at about 600 F., and thereby respond and indicate the existence of an overheat condition below the temperature at which a fixed temperature fire condition is detected, as will be made apparent hereinafter. As mentioned before, when the temperature of the resistor 12 decreases, the resistance of this resistor increases rapidly to rapidly unbalance the bridge network to the off direction, whereby resetting is efiected. For example, the resistance of the resistor 12 increases from about 6.8 kilo-ohms at 600 F. to about 37 kilo-ohms at 500 F.

In Fig. 5, the ambient temperature conditions to which the detecting resistor 12 would be subjected during a typical flight of a jet plane are represented by the unbroken line, wherein various sections between points indicate the following particular stages of the flight:

ab Warmup and take-ofl. b--c Cooling in level flight. cd Level flight.

d.e Combat maneuver. ef Return to level flight. f-- -g Level flight.

gh Descent for landing. h-.-i Approach for landing. i--j Taxiing.

jk Run up to hangar. k-l Cooling 011.

dition due to a fire which the resistor 12 senses. The.

peak B represents a rise in temperature at a slow rate which an overheat condition would produce. The peak C represents a rise in temperature at a slow rate which a smoldering fire would produce. These conditions and the effect thereof on the detecting network will now be described with reterence to Figs. 1 to 4.

In Fig. 1, the network is shown in its normal or nonoperated condition while the temperature which the resistor 12 senses is below 600 F. and the rate-of-rise due to overheat above 530 F. is not sufliciently rapid to be detected. Both of the indicators 17 and 18 are in their off position, the relays 23 and 24 are not energized and their switch means are open except that the element 30 engages the contact 31, and both of the lamps 36 and 47 are unilluminated or dark.

In the event a temperature condition occurs which is simulated by the peak A, whereby a rapid rise in temperature is sensed as in the case of a sudden burst of flame, the rise in temperatureabove 530 F. causes the rate-of-rise network to change the polarity sensed by the indicator 17, whereby this indicator goes to its on position, as shown in Fig. 2, and effects operation of the elay 23 and illumination of the lamp 36 under the control of this relay.

If the flame goes out quickly by itself, the temperature of the sensing resistor drops and its resistance increases to cause the indicator 17 to return to its initial position shown in Fig. 1, whereby the relay 23 is de-energized and the lamp 36 goes out. Likewise, if the rise in temperature ceases or is at a slower rate than can be sensed by the rate-of-rise network, the indicator 17 returns to its initial position (Fig. 1). However, should the temperature sensed go above 600 F. (without further rateof-rise detection), the polarity sensed by the indicator 13 is changed whereby this indicator goes to its on position, as shown in Fig. 3, and efiects operation of the relay 24 and illumination of the lamp 47 which is now connected across the conductors 10 and 11 through switch element 30, contact 31, switch element 45 and contact 46 and indicates a post-fire overheat condition. If the temperature sensed goes above 700. F. (with or without rate-of-rise detection) the indicator 17 again goes to its on position as shown in Fig. 4, to operate the relay 23 which causes the switch element 30 to disengage its contact 31 to put out the lamp 47 and causes the element 30 to engage its contact 32 to illuminate the lamp 36.

The peak B represents a slow rise in temperature created by an overheat condition above 600 F. This simply causes the network to change from the condition shown in Fig. l to that shown in Fig. 3 with only the lamp 47 being illuminated.

The peak C represents a slow rise in temperature created by a smoldering fire. As the temperature goes above 600 F., the lamp 47 is illuminated (Fig. 3) and, when the temperature goes above 700 F., the lamp 36 is illuminated and the lamp 47 goes out (Fig. 4).

Thus, by noting which lamps are illuminated and the sequence of illumination thereof, various temperature conditions can be discriminated to determine their cause, as illustrated by the table about to follow.

Cause 1. Flaming fire:

A. Momentary 36 on36 oii. B. Momentary with overheat 36 on36 0112-47 on--47 olf. C. Enduring- 36 on36 otT47 on47 otf36 on36 off 47 on47 oft. II. Overheat: 47 on47 011. III. Smoldering fire:

47 on 47 off-36 on36 off-47 on47 ofl.

From this table, it will be observed that each time an enduring first of the flaming or smoldering type is indicated by sensing a temperature above 700 F., a post-fire overheat condition is indicated which indication in most cases will endure only momentarily because extinguishrnent of the fire also may rapidly cool the sensing resistor temperature conditions. T

' debating from the "s irit and scope or the' tinvention' and I tthanfmomentarily cause the "same to be so oprated.

' from the'j'foregoing descri tion, it will? be' seen that thefpresent invention "provides 'asim' fle; ractical; and I reliable network fordiscrimrnsting-theeauses of various provide 'a pair of voltage" dividing bridges norinallv iin balanced in one direction and said first resistance elemen't'being constructed and'arranged sothat theresistance thereof changes inresponse to a' predeterminedicondif tionlto another value whereby the bridges goftowards" unbalance in the opposite'directioman electromagneticallv, operable device connected in voltagedividing.relationship facross saidthird element anddhe junctioniofjsaid first and second elements, and a second electromagneticaliy operable device connected infvoltage dividingrre lationship across said fourth element andth-iunction'of said first and second elements. a J 2. A system accordingto claim 1, 'wherein aid thirdt t element has a much lower resistance valile:than saidf fourth "element to expedite resetting of said first elect'ro magnetically operable device; :1 3. A system according to claiml wherein the van-age." dividing relationship of "said ifthird and fourth elenients canbeadjusted. .7 a a V I 4. A systenraccordingto claim 1,- including .a-s ignal circuitfo'r each'of said elctromagnetically operable de vices and under the controlthereoflj a t SJA systemaccordingcto-claim l,wher e i n eachof; said electromagnetically loperableldevieesincludes a pair; of switch contacts, one"connected to each sideot: ssource, and a switclr'arm for selectivelynengaging said; contacts connected through a .diode tsunam itsaid; source; a relay having a switch contactganda switcli arm is connected acrossttheda stmentioned side oftisaid source and each of said switehxarms; and signal device is connected across the la st rnentioned side offsaid source and each "of said relayswitch contacts; one of-said -relays having aisecond switch contact andhaving itsswitch fourthfelement 'and 'theijunction of said first a nd secondelefilmsll-- or a a, Y.

7. Ina sy stei n for detecting heat due to var ous causes;v

the combinationfoffa source of unidirectional; currengi first' 'fandTsecond'i'esistance elements connected m'serles across" said jsem'eey parallel third and fourth resistance element's"and"anothr resistance element connected in seriesttherewith across said source, said elements havingresi'stance'values to provide a pair of voltage dividing j bridges, said bridges 'being ir'normally unbalancedin; one I 7 direction and'fsaid first element being, constructed ,and

arrangdso thatthe resistance decreases in response toa A v predeterminedth ghr temperature condition to another value whereby th'bridg'es go towards'unbalance in theopposite direction, 'a time constant network includingelectromganeticallyl operable device connected in voltage? dividing fre'l'ationship across said third element and the junctionofsaid fifst and second elements for indicating a fire, 'a'ri "second"electromagneticallv operable device; connected m' vol'ta'ge 'diiiiding relationship across said fourth "elemeiit'and' the ju'nrition' of said first and second 1 elementsrdrirrdieatinganoverheat condition. j a

8. A system according to 7, including ajsigfial' l circuit for 'ach'fof' said" elcti'omagnetically' operable 'de- I vices and under the control thereof so-arrangedandinterrelat'ed to discriminate "between a sudden fire, an overheatcondi'fioriandjafs "lysbu' r'nmg' fire. a I

9; 'Asysterh according "to"clain17,' wherein said 'ele resistance values, whereby said "first device 7 responds" a sudden 'fire jab'oTve a iven-tempera ureievel and "res esfroi a slo'wlyrburni glfii'eab'ove'a higher; temperatu e levelg and saidis'e'conddevice' responds sang overheat condition Taliov' an's intermediate temperature level; N

to claim: 10, wherein easier said electromagneticallyfoperabledevices includes" a" pair 7 of switch cont'a'ctsres'pectivelyf connectedto sides of said source and a witch 'arrn idr"selectivityengaging said contacts connectedthrough a diode'to one side of 'said T source, a relay is'co'nn'ec'ted across the last inentio'ned'fside' t:

of said source and each of said switchj"arinshavirig"a switch contact andfa swi't'ch"'arrii; andi'a sig'n'aldev ce is connected acros's'thelasfinentionedj side'of 'saiasource T and each of said relayfswitch c'ontacts,jone'ofsaidrelays having a "second""'swit'ch cemacrand "having its "swi arm connected to the other side of-said 'sourc'eg'saids'e" ond switch contact being connected to'said 'switch arm of said other relay. t

12. In a system for detecting heat d to vaai1scauses, the combination of a sourcefof"unidirectional'cur second switch contact beingsconnected; to said; switc arrnconnected'tov the otherls'ide'ot 'sai d s ourcefsa" rent, first and second resistance elements connected in? series across said source, third, fourth and resistance elements connected in parallel-seriesacross San source, said elements having resistance valuestd provid 'a'paif of voltage dividing bridges in which said first, secondand" fifth elements are common thereto, said brid'ge's being normally unbalanced in one direction and said firstele merit-beingconstructed and arranged s that' 'the resistance decreases n fre'sponse to an increase I in temperature to another value whe'fehv Y the bridges go towiards unbalance" in the opposite d'n; anl oniagneti'callj iopera ble device connected "involtage dividing relationship across saidthird elementand the junction of said first'and sec'dnd elements'fforindicatinga "fifej'and a second electromag f: 'netically operable device connected in ivoltageldividing' 7 relationship across said-fourth'elernentandlthe junction of said first and second ,elenaemsro'r indicating an over:

heat condition.

arm of'said' other relay. A

6. In a condition responsive system, the combination of a source of unidirectional current, firstand fsecond resistance elements connected in series 'across'said "source, third, fourth and-fifth resistance elements?connect'ed iin parallel-series across said source, saidf-i'eletnents'having resistance values to provide a pair of vo'ltagei-.-dividing bridgeslin whichsaidt-first second an'd fifth-elements are common thereto, said bridges being m riially tinbalanced in one direction and said first el'e'inene'be' a oiistruc edf and arranged so that the resistance thereofehan'g'e -m response to a predetermined conditiontd anothef value whereby the-bridges g r==towards unbalance-finithe op i positedirection, :an -electrornagnetical ly-zoperable device: connected 1 in voltage": "dividing-urelationshipge'across z-saidi third element- 1 and -thea -junetion of said first and seeo'ri elerrrents,": and a secondlectromagnetically OperabTe device 'connect'ed' in voltage dividing' relat'ionship a'cross said (Refei'cnceswrfollowing p gy i Refereaces Cited in the file of this patent 2,577,973 MacDougall et a1 Dec. 11, 1951 UNITED STATES PATENTS 2,587,762 Ree? M 1952 2,236,891 Bridges Apr. 1, 1941 FOREIGN PATENTS 2,535,133 Hoch Dec. 26, 1950 5 250,589 Great Britain Apr. 7, 1926 

